This was originally destined to be an “in my not-so-humble opinion” piece, but in the process of researching the origins of this recommendation, I actually managed to find a legit professional medical opinion — from the American College of Obstetricians and Gynaecologists (ACOG), no less — that rebukes it. Even better, the opinion came from one of the doctors originally involved in the development of said guideline. How’s that for myth-busting?

First little bit of history about how it came to be believed that pregnant women should not allow their heart rates to exceed 140 beats per minute during exercise:

Back in the early 80’s, when target heart rates were the gold standard for measuring exertion during exercise, Dr. Raul Artal and a group of colleagues from the ACOG developed a video on exercise during pregnancy. “We had to come up with a guideline in a short period of time,” said Dr. Artal. “Nobody had data on pregnancy so we guesstimated. There is no science to support this.”

In 1994, the ACOG quietly removed this recommendation from their updated guidelines for pregnancy exercise, and in 2002 they publicly rescinded it. So there you have it, folks.

Sadly, the Canadian Society of Exercise Physiologists and the Society of Obstetricians and Gynaecologists of Canada is still proliferating recommendations based on a mere “guesstimate” that is now more than 17 years out of date. In their 2003 Joint Practice Guideline, Exercise in Pregnancy and the Postpartum Period, they suggest a target heart rate varying between 120-155 beats per minute, depending on maternal age. Their rationale? “There is an increase of 10 to 15 beats per minute in resting heart rate in pregnancy. However, at maximal exercise levels, there is a blunted heart rate response as compared to the non-pregnant state.”

Of course, an increased heart rate during exercise is an essential and desirable physiological response that allows the body to deliver greater quantities of oxygen-rich blood to its tissues. I extrapolate, then, that the real concern about a blunted heart rate response is in fact a concern about a potential shortage of oxygen to the developing fetus. But notice that this blunted heart rate response occurs at maximal exercise levels, which the average woman never approaches (CrossFitters, on the other hand… ;)).

So, how is a woman to gauge a safe level of intensity for exercise during pregnancy? Newer guidelines suggest using the Rate of Perceived Exertion (RPE) scale, and aiming for “moderate to hard” exertion (4-6 on the 10-point scale, and 12-14 on the 20-point Borg scale).

Source: coachsci.sdsu.edu

An even easier way to think of it is that you should be working at least hard enough that you aren’t able to sing, but not so hard that you’re too winded to speak a few words.

So then, what is a dedicated CrossFitter to do when the whole notion of CrossFit centres around maximally intense effort at all times? Simple: just tone it down. The definition of CrossFit is “constantly varied functional movements executed at high intensity.” I would say that CrossFit during pregnancy is “constantly varied functional movements executed at moderately high intensity.”

Here are some suggestions for how to reduce intensity and still get a decent workout. While my recommendations are geared towards the CrossFit set, they can be adapted and applied to any exercise regimen you choose:

1. Maintain a pace where you can still speak a few words at a time. During pregnancy, you should not be so winded that you are left gasping for air. If you are struggling to get enough oxygen, chances are that your precious cargo is as well.

2. Stop the clock. Pregnancy is not a time to be trying to set gym records, or even personal records, for that matter. Instead of doing a prescribed workout “for time,” just do the workout — without running the timer — at whatever pace you feel comfortable.

3. Stick to “work priority” versus “time priority” workouts. Avoid workouts that require you to complete as many reps/rounds as possible in a specified period of time. Instead, choose a set amount of work and just do it.

4. Rest. Don’t be afraid to stop and catch your breath or take a drink. Not only do you have to ensure a sufficient supply of oxygen to the fetus, you also need to ensure that your body doesn’t overheat, especially in warmer climates. An increase in maternal body temperature of even a couple of degrees (especially during the first trimester) is correlated with an elevated risk of fetal developmental problems and spontaneous abortion (miscarriage). Pregnant women are also at greater risk of dehydration, so don’t feel guilty about stopping to have a few sips of water.

5. Listen to your body. During pregnancy, every day is different. Some days you’ll be exhausted just walking from your car to the gym, and other days you’ll be feeling fantastic and ready to kick ass. Go with the flow. If you need to scale back the reps on a long “grinder” workout, do so. If you need to reduce a five round workout to three rounds, that’s okay. And if your body tells you that it really needs a nap more than it needs a workout, well then take the darn nap and enjoy it! (I know I sure did… many times :))

At the end of the day, even with the intensity taken down a few notches, a CrossFit-based prenatal fitness program will go a long way towards maintaining your fitness, preventing excessive weight gain, improving morale and body image, reducing pregnancy-related health complications, and improving the odds of a smooth labour and delivery.

Just do yourself a favour and leave the heart rate monitor at home.

Workout:

SATURDAY

Practice sets of 2 split jerks (one per side). I was only able to get one rep out at 135 lbs, which was a little frustrating since I definitely know that I can — or at least could — clean and jerk my pre-pregnancy body weight of 155 lbs. But my technique was pretty solid today, so I suppose that’s something.

“Nancy” (five rounds of 400 m run and 15 overhead squats @ 65 lbs) – 19 min 41 sec. I did the runs at a fairly moderate pace, partly prevent getting winded and partly because it was raining and the corners of that parkade gets damn slippery when it’s raining (don’t really need an ankle sprain right now!).

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Thank you for this! I continued to play soccer after I discovered I was pregnant (sadly it ended in miscarriage) and was constantly worried about my heart rate getting too high. Next time I won’t worry about that!

ABOUT ONE FIT MOM

Hi, I'm Carli -- a fitness and nutrition enthusiast and mom of two, living in beautiful Vancouver, Canada.

I started this blog when as a Paleo-eating Crossfitter, I found myself pregnant with my first child. All of the conventional pregnancy guidelines for nutrition and exercise just didn't jive with what I knew to be healthy for me. So I charted my own course and decided to document my journey for others who might be interested in following a similar path.